The use of rare earth phosphors for general illumination fluorescent lamp applications is well known. Rare earth phosphors contain at least one rare earth element, typically as the activator ion (e.g., Eu2+, Tb3+, Ce3+). Every manufacturer of such lamps uses rare earth phosphors to produce lamps with different levels of light output (lumens), color temperature (CCT) and CRI. Typical rare earth phosphors in commercial use for fluorescent lamps include the red-emitting Y2O3:Eu (YOE), the green-emitting La(PO4):Ce,Tb (LAP) and the blue-emitting BaMgAl10O17:Eu (BAM). Other green-emitting phosphors such as (Ce,Tb)MgAl11O19 (CAT) and (Gd,Ce,Tb)MgB5O10 (CBT) and blue-emitting phosphors such as Sr5(PO4)3:Cl,Eu (SCAp) are also known to practitioners of the art.
While the use of rare earth phosphors in discharge lighting is well known, the trend in the industry has been to use to smaller and smaller size phosphors in order to reduce the powder weight needed for a given level of lumen output. However, it also has become increasingly desirable to produce higher efficacy light sources in order to reduce energy consumption and thereby reduce greenhouse gas emissions.
A higher efficacy light source would have a higher LPW (lumens per watt of electrical power input). Using a fluorescent lamp with a higher LPW would reduce the consumption of electrical energy (KWh) for a given level of light output. Less consumption of electrical energy by consumers in all categories would result in a decrease in the quantity of fossil fuel usage at the electric power utilities. This in turn would lower the amount of CO2 greenhouse gas generated by the combustion of fossil fuels.